1. Field of the Invention
The present invention relates to a hydrogen sensor, particularly to a hydrogen sensor for measuring the concentration of hydrogen gas in a fuel gas for use in a fuel cell.
2. Description of the Related Art
In response to concerns about global environmental pollution, in recent years intensive studies have been conducted on fuel cells for use as high-efficiency, clean power sources. Among such fuel cells, a polymer electrolyte fuel cell (PEFC) shows promise for automobile use and household use, by virtue of its inherent advantages, such as operation at low temperature and high output density.
A promising fuel gas for use in PEFC is a reformed gas reformed from methane, methanol, gasoline, etc. In this connection, in order to enhance efficiency and the like factor, a sensor capable of directly detecting hydrogen in the reformed gas must be provided. Since this gas sensor is used in a hydrogen rich atmosphere, an operating temperature thereof must be low (about 100° C. or lower).
Such a sensor of low-temperature operation type is proposed in, for example, European Patent Publication No. 1103807A2. As shown in FIG. 9, the proposed sensor employs a proton conduction layer P1 formed from a polymer electrolyte and is configured such that a first electrode P2, a second electrode P3, and a reference electrode P4 are disposed on the corresponding surfaces of the proton conduction layer P1, and the resultant assembly is held between a pair of support elements P5 and P6.
However, the above-mentioned publication does not mention a method for sealing (a method for maintaining gastightness of) a measurement chamber P8, into which a fuel gas (thus hydrogen gas) is introduced via a diffusion controlling portion P7, nor does it mention a method for fixing the support elements P5 and P6.
Conceivably, a resin-adhesive such as epoxy may be used for sealing and fixing, as in the case of FIG. 9, in which the proton conduction layer P1 and the support elements P5 and P6 are fixed together by means of the resin adhesive P9. However, this method does not necessarily provide sufficient heat resistance and durability, causing a leakage of hydrogen through the adhesive P9.